Method of producing refractory metals



Patented Feb. 14, 1928.

UNITE STATES P rice.

ERNEST ANTON LEDERER, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTING- HOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

METHOD OF PRODUCING REFRACTORY METALS. I

No Drawing.

This invention relates to a method of producing refractory metals and more particularly to the production of such metals as tungsten and molybdeum in a pure coherent condition.

Heretofore, the method commonly employed for obtaining refractory metals has been by the reduction of the oxide thereof. For instance, tungsten for commercial usage is produced substantially entirely by the reduction of tungstic acid in hydrogen, the

resultant metal powder being pressed into slugs and sintered in an atmosphere of hydrogen.

In this process the metal both in the sintering and in the reduction process, is highly heated in intimate contact with hydrogen, and may become more or less contaminated thereby. Moreover, since the tungsten is produced from the oxide thereof, there may remain in the reduced powder, a small amount of the oxide. Both hydrogen and oxygen, even in minute quantities deleteriously affect the metal, particularly for use in producing filaments for incandescent electric lamps and while these impurities may be removed from the surface portions of the metal by proper treatment, nevertheless, since it is the powdered tungsten which is most likely to become contaminated thereby, prior to the production of the slug, the impurities may be present in the interior of the slug and hence not readily removable.

In producing the slugs from the powdered tungsten metal, it is necessarv to exert extremely high pressures thereon to render the powder sufficiently coherent to withstand the handling incident to the sintering of the slug. These pressures, which are in the neighborhood of 40,000 pounds per square inch necessitate the use of large and expensive hydraulic presses. One of the objects of the present invention is to provide an improved process of producing refractory metals free from such impurities as hydrogen and oxygen.

Another object is to produce a slug of refractory metal in a coherent state without the necessity of applying excessive pressures thereto.

, Another object is to provide an improved process of obtaining tungsten or molybdenum in a pure condition.

Another ob ect 1s to produce a dense co- Application filed November 22, 1924. Serial No. 751,678.

The pure sulphides of the refractory. metals may be pressed into slugs at moderate 1 pressures and heated in a vacuum or in a reducing atmosphere, such as hydrogen, to completely reduce the same, the resultant slug consisting of pure coherent tungsten either in a spongy or dense condition dependent upon the heat treatment given thereto as will appear more fully hereinafter. The tungsten so produced is entirely free from such impurities as oxygen, carbon, sul phur. etc. and when reduced in a vacuum is also free from hydrogen. In this extremely pure condition, the tungsten is ductile and may be rolled, swaged or drawn into wires or incandescent electric lamp filaments.

If desired, the sulphide of refractory metal may be coated on a core of metal or other material and reduced in situ to form a refractory metal coating therefor, or the sulphide may be reduced in powdered form and a finely divided tungsten powder obtained therefrom.

Other uses of refractory metals produced by the reduction of the sulphides thereof Will be readily apparent to those skilled in the art. I

In order that this invention may be more fully understood, the process which I have found preferable for producing pure retractory metals, will be set forth in detail and while the process will be described as applied particularly tothe production of tungsten, it will be understood that it applies equally well to the production of other rofractory metals.

Tungsten .disulphide 1s a black crystalline substance having physical properties somewhat similar to graphite and it may be readily prepared in a chemically pure condition by heating a mixture of tungstic acid and an alkaline carbonate such as potassium or sodium carbonate andsulphur at a dull red. heat for one or two hours out of contact with the atmosphere preferably in a cruciv ble in a gas blast furnace. Since this process is well known in'the art, it need not be described in further detail herein.

produce a slug sufficiently coherent to sustain itself and permit the same to be readily handled. In practicing this inventlon, tungsten disulphide was pressed in a mold, in

a small hand vise and slugs thereof produced having a coherency about the same as that ofchalk, which were capable of being readily handled during the subsequent operations. For convenience in treating, the slug may be of the size commonly employed in the production of slugs from powered metallic tungsten for wire drawing purposes, namely about eight inches long and about onequarter inch square, in cross section. It should be borne in mind that during the process of reduction of the sulphide and in the subsequent sintering process, that the slug decreases to about half its original cross section.

The pressed slug should be heated either in a vacuum or in hydrogen at a temperature suificiently high to cause complete reduction of the sulphide. The tungsten disulphi e may be reduced in hydrogen at temperatures ranging from 800 C. to 1000 C. while the heat required to decompose the same in a vacuum is about 1200 C. I prefer to carry out the reduction of the sulphide in a vacuum since the opportunity of the metal produced thereby becoming contamimated with hydrogen, is eliminated.

The reduction may be carried out in a vacuum electric furnace preferably a furnace using tungsten spiral heating elements rather than carbon heating elements in order to eliminate any opportunity of carbon being present in the reduced slug. The heating should be started around 800 C. and

the temperature gradually increased to about 150 0 which latter temperature may be maintained for about one-half hour or until the sulphide is completely reduced. Care of the slug which would hinder or prevent the escape of sulphur from the interior thereof.

-The product obtained at this stage of the process is a pure coherent slug of spoiwy tungsten.' If desired, the process might e stopped at this point and the spongy tungsten utilized for various purposes, such as catalysts.

In order to consolidate the slug and produce a dense bar of tungsten, the temperature should be gradually raised to about of the melting point of the metal which in the case of tungsten, is about 3400 C. and in the case of molybdenum about 2400 C. At these temperatures, the spongy mass is sintered into an extremely dense pure body of tungsten metal.

The slugs of tungsten or molybdenum disulphide are conductive and in place of-heating the slugs in the electric furnace, they may be heated electrically by passing a current therethrough in a vacuum or in hydrogen in the same manner as the pressed slugs of powdered tungsten are sintered at the present time. g 1

It will be noted that the slug is produced directly from the tungsten compound in a single heat treatment out of contact with any contaminating influences such as hydrogen, oxygen, or carbon and since the metal is obtained by the reduction of a compound which contains none of these elements, there will be neither carbon, oxygen nor hydrogen present in the finished slug. Moreover, by proper heat treatment of the slug, during I reduction,'the shlphur will be entirely eliminated therefrom and 'a bar of pure tungsten produced which is ductile and hence capable of being swaged and rolled into various forms or drawn intowire.

It should be further noted that the pure coherent tungsten may be produced either in a spongy or in a dense condition.

While only the preferred method of carrying out this invention is described herein, 1t 3 is to be understood, of course, that many changes may be made in the invention without,departing therefrom.

What is claimed is:

1. The method of producing highly rci fractory metals which consists in heating a sulphide of the metal in a vacuum to the decomposition temperature and removing the volatilized sulphur.

2. The method of producing coherent refractory metals which consists in agglomerating a sulphide of the metal, heating the sulphide to the decomposition temperature in an environment substantially inert with respect to the metal'and removing the volatile constituent.

3. The method of producing coherent refractory metals which consists in pressing a sul hide of the metal into a coherent form and heating the sulphide in a vacuum tode- 1 compose the same while maintaining said vaeuous condition.

4. The method of producing substantially pure tungsten which consists in heating an agglomerated mass of a sulphide of tungsten to the decomposition temperature in the absence of contaminating influences.

5. The method of producing substantially pure tungsten which consists in heating a sulphide of tungsten to the decomposition temperature in a vacuum.

6. The method of producing coherent bars of tungsten which consists in pressing tungsten disulphide into compact slugs and reducing the tungsten disulphide by heating to the dissociation temperature in an environment inert with-respect to the tungsten metal.

7. The method of producing coherent bars of refractory metals which consists in pressing a sulphide of the metal into compact slugs and reducing the sulphides of the metals by heating to the dissociation temperature out of contact with contaminating in fiuenees. v

8. The method of producing coherent bars of substantially pure refractory metal which consists in pressing a sulphide of the metal into slugs and heating the same in a vacuum at a temperature sufliciently high to reduce the sulphide of the metal, without causingsintering of the metal.

9. The'method of producing coherent bars of substantiallypure refractory metal which consists in pressing a sulphide of the metal into slugs, heating the slugs in a vacuum at a temperature below the sintering temperature of the metal for a suflicienttime to completely reduce the sulphide of the metal, and thereafter sintering the slugs into a dense bar. i 10. The method of producing coherent bars of substantially pure tungsten whichconsists in pressing tungsten disulphide into slugs, heating the slugs in a vacuum at a temperature below the sintering temperature of the metal for a. sufficient time to completely reduce the sulphide of the metal, and thereafter sintering the slug into a dense bar.

In testimony whereof, I have hereunto subscribed my name this 21st day of November, 1924.

ERNEST ANTON LEDERER. 

